Age measurements of the Precambrian rocks of the Death Valley-Mojave Desert region, California

Ar^(40)-K^(40) and Sr^(87)-R^(87) age measurements in the eastern Mojave Desert indicate two separate early Precambrian events (see table). The older event is approximately 1650 m.y. old and is evidenced by pegmatites and associated metamorphic rocks in the Mountain Pass district. Ages were measured on coarse muscovite and potassium feldspar, MP-1 and MP-2, from a pegmatite which cuts across biotite-bearing gneisses, MP-7 and MP-9. These data confirm the widespread areal extent of this ancient metamorphic terrane. Ages of biotite, MP-21 and MP-22, from the shonkinite, which intrudes the metamorphic rocks, at Mountain Pass and the Rb-Sr age of potassium feldspar, MM-3f, from granite in the Marble Mountains suggest a period of igneous intrusion in the 1350 to 1410 m.y. interval. Metamorphic rocks in the central Panamint Range have been mapped and are shown to be stratigraphically early Precambrian. K-Ar ages of approximately 80 m.y. have been measured on biotite, muscovite, and hornblende. The minerals show no memory of a Precambrian age. The early Precambrian rocks show no evidence of a younger period of metamorphism. However, a younger metamorphism can be recognized in the overlying Precambrian(?) Noonday dolomite and Johnnie formation

Correlation of Ordovician and Silurian Formations of Eastern Montana

Correlation charts made from electric log data show the relationship of Ordovician and Silurian strata in eastern Montana. The Silurian sediments terminate westward in eastern Montana, but the Ordovician sediments are present westward into central Montana

I. Geology of the Wildrose area, Panamint Range, California. II. Geochronologic studies in the Death Valley-Mojave Region, California

The bedrock in the Wildrose area is predominantly a sequence of metamorphosed sedimentary and possible volcanic rocks that is more than 15,000 feet thick. All the metamorphic rocks are Precambrian in age on stratigraphic evidence. The rocks are divided into three age groups, early Precambrian, later Precambrian, and Precambrian (?), that are separated by unconformities. The early Precambrian Panamint metamorphic complex has been divided into two series that are separated by a profound unconformity. Small stocks and dikes of granitic rocks, which are presumably Cretaceous in age, intrude the metamorphic rocks. Tertiary sedimentary rocks and Quaternary alluvium are also present in the area. The structural features of the area are ascribed to four periods of deformation. The large folds in the early Precambrian rocks and associated minor folds were produced during the first two periods of deformation of early Precambrian age. Low angle faults are evidence of the third deformation which is considered to be Cretaceous in age. The fourth period of deformation produced high angle faults. Movement along the high angle faults began in late Tertiary time and has continued to the present. All the Precambrian rocks of the area have been affected by middle or lower middle grade metamorphism. Even though structural evidence suggests that metamorphism must have accompanied the earlier periods of deformation, the present mineral assemblages reflect the third period of deformation which, on the basis of mineral age measurements, was Cretaceous in age. Narrow contact metamorphic aureoles surround the larger masses of granite. Radioactive ages were measured in five areas in the Death Valley-Mojave Desert region. The rocks are Precambrian in age on stratigraphic evidence in three areas, the Wildrose area of the Panamint Range, the Mountain Pass district, and the Marble Mountains. The rocks in Joshua Tree National Monument and the Kilbeck Hills are presumably Precambrian, but no stratigraphic evidence of their age has been found. The geochronologic studies in the five areas indicate three distinct groups of K - Ar and Rb-Sr ages. Ages of approximately 1650 million years are obtained on metamorphic rocks and associated pegmatite s in the Mountain Pass district. Younger igneous rocks at Mountain Pass and in the Marble Mountains have age patterns that are interpreted to indicate intrusion in the 1350 to 1450 million year interval. Metamorphic rocks in the Wildrose area, Joshua Tree National Monument , and the Kilbeck Hills have ages in the 75 to 85 million year interval which are interpreted as the age of regional metamorphism related to the Cretaceous Nevadan orogeny. An age of 73 million years was obtained on a post-metamorphic granite

Geologic map of part of the Marble Mountains, San Bernardino County, California: Supplement 4 from "I. Geology of the Wildrose area, Panamint Range, California. II. Geochronologic studies in the Death Valley-Mojave Region, California" (Thesis)

The bedrock in the Wildrose area is predominantly a sequence of metamorphosed sedimentary and possible volcanic rocks that is more than 15,000 feet thick. All the metamorphic rocks are Precambrian in age on stratigraphic evidence. The rocks are divided into three age groups, early Precambrian, later Precambrian, and Precambrian (?), that are separated by unconformities. The early Precambrian Panamint metamorphic complex has been divided into two series that are separated by a profound unconformity. Small stocks and dikes of granitic rocks, which are presumably Cretaceous in age, intrude the metamorphic rocks. Tertiary sedimentary rocks and Quaternary alluvium are also present in the area. The structural features of the area are ascribed to four periods of deformation. The large folds in the early Precambrian rocks and associated minor folds were produced during the first two periods of deformation of early Precambrian age. Low angle faults are evidence of the third deformation which is considered to be Cretaceous in age. The fourth period of deformation produced high angle faults. Movement along the high angle faults began in late Tertiary time and has continued to the present. All the Precambrian rocks of the area have been affected by middle or lower middle grade metamorphism. Even though structural evidence suggests that metamorphism must have accompanied the earlier periods of deformation, the present mineral assemblages reflect the third period of deformation which, on the basis of mineral age measurements, was Cretaceous in age. Narrow contact metamorphic aureoles surround the larger masses of granite. Radioactive ages were measured in five areas in the Death Valley-Mojave Desert region. The rocks are Precambrian in age on stratigraphic evidence in three areas, the Wildrose area of the Panamint Range, the Mountain Pass district, and the Marble Mountains. The rocks in Joshua Tree National Monument and the Kilbeck Hills are presumably Precambrian, but no stratigraphic evidence of their age has been found. The geochronologic studies in the five areas indicate three distinct groups of K - Ar and Rb-Sr ages. Ages of approximately 1650 million years are obtained on metamorphic rocks and associated pegmatite s in the Mountain Pass district. Younger igneous rocks at Mountain Pass and in the Marble Mountains have age patterns that are interpreted to indicate intrusion in the 1350 to 1450 million year interval. Metamorphic rocks in the Wildrose area, Joshua Tree National Monument , and the Kilbeck Hills have ages in the 75 to 85 million year interval which are interpreted as the age of regional metamorphism related to the Cretaceous Nevadan orogeny. An age of 73 million years was obtained on a post-metamorphic granite

Index and locality map, Death Valley-Mojave Desert region: Supplement 3 from "I. Geology of the Wildrose area, Panamint Range, California. II. Geochronologic studies in the Death Valley-Mojave Region, California" (Thesis)

The bedrock in the Wildrose area is predominantly a sequence of metamorphosed sedimentary and possible volcanic rocks that is more than 15,000 feet thick. All the metamorphic rocks are Precambrian in age on stratigraphic evidence. The rocks are divided into three age groups, early Precambrian, later Precambrian, and Precambrian (?), that are separated by unconformities. The early Precambrian Panamint metamorphic complex has been divided into two series that are separated by a profound unconformity. Small stocks and dikes of granitic rocks, which are presumably Cretaceous in age, intrude the metamorphic rocks. Tertiary sedimentary rocks and Quaternary alluvium are also present in the area. The structural features of the area are ascribed to four periods of deformation. The large folds in the early Precambrian rocks and associated minor folds were produced during the first two periods of deformation of early Precambrian age. Low angle faults are evidence of the third deformation which is considered to be Cretaceous in age. The fourth period of deformation produced high angle faults. Movement along the high angle faults began in late Tertiary time and has continued to the present. All the Precambrian rocks of the area have been affected by middle or lower middle grade metamorphism. Even though structural evidence suggests that metamorphism must have accompanied the earlier periods of deformation, the present mineral assemblages reflect the third period of deformation which, on the basis of mineral age measurements, was Cretaceous in age. Narrow contact metamorphic aureoles surround the larger masses of granite. Radioactive ages were measured in five areas in the Death Valley-Mojave Desert region. The rocks are Precambrian in age on stratigraphic evidence in three areas, the Wildrose area of the Panamint Range, the Mountain Pass district, and the Marble Mountains. The rocks in Joshua Tree National Monument and the Kilbeck Hills are presumably Precambrian, but no stratigraphic evidence of their age has been found. The geochronologic studies in the five areas indicate three distinct groups of K - Ar and Rb-Sr ages. Ages of approximately 1650 million years are obtained on metamorphic rocks and associated pegmatite s in the Mountain Pass district. Younger igneous rocks at Mountain Pass and in the Marble Mountains have age patterns that are interpreted to indicate intrusion in the 1350 to 1450 million year interval. Metamorphic rocks in the Wildrose area, Joshua Tree National Monument , and the Kilbeck Hills have ages in the 75 to 85 million year interval which are interpreted as the age of regional metamorphism related to the Cretaceous Nevadan orogeny. An age of 73 million years was obtained on a post-metamorphic granite

Structure sections, Wildrose area, Panamint Range, California: Supplement 2 from "I. Geology of the Wildrose area, Panamint Range, California. II. Geochronologic studies in the Death Valley-Mojave Region, California" (Thesis)

The bedrock in the Wildrose area is predominantly a sequence of metamorphosed sedimentary and possible volcanic rocks that is more than 15,000 feet thick. All the metamorphic rocks are Precambrian in age on stratigraphic evidence. The rocks are divided into three age groups, early Precambrian, later Precambrian, and Precambrian (?), that are separated by unconformities. The early Precambrian Panamint metamorphic complex has been divided into two series that are separated by a profound unconformity. Small stocks and dikes of granitic rocks, which are presumably Cretaceous in age, intrude the metamorphic rocks. Tertiary sedimentary rocks and Quaternary alluvium are also present in the area. The structural features of the area are ascribed to four periods of deformation. The large folds in the early Precambrian rocks and associated minor folds were produced during the first two periods of deformation of early Precambrian age. Low angle faults are evidence of the third deformation which is considered to be Cretaceous in age. The fourth period of deformation produced high angle faults. Movement along the high angle faults began in late Tertiary time and has continued to the present. All the Precambrian rocks of the area have been affected by middle or lower middle grade metamorphism. Even though structural evidence suggests that metamorphism must have accompanied the earlier periods of deformation, the present mineral assemblages reflect the third period of deformation which, on the basis of mineral age measurements, was Cretaceous in age. Narrow contact metamorphic aureoles surround the larger masses of granite. Radioactive ages were measured in five areas in the Death Valley-Mojave Desert region. The rocks are Precambrian in age on stratigraphic evidence in three areas, the Wildrose area of the Panamint Range, the Mountain Pass district, and the Marble Mountains. The rocks in Joshua Tree National Monument and the Kilbeck Hills are presumably Precambrian, but no stratigraphic evidence of their age has been found. The geochronologic studies in the five areas indicate three distinct groups of K - Ar and Rb-Sr ages. Ages of approximately 1650 million years are obtained on metamorphic rocks and associated pegmatite s in the Mountain Pass district. Younger igneous rocks at Mountain Pass and in the Marble Mountains have age patterns that are interpreted to indicate intrusion in the 1350 to 1450 million year interval. Metamorphic rocks in the Wildrose area, Joshua Tree National Monument , and the Kilbeck Hills have ages in the 75 to 85 million year interval which are interpreted as the age of regional metamorphism related to the Cretaceous Nevadan orogeny. An age of 73 million years was obtained on a post-metamorphic granite

Geologic map of the Wildrose area, Panamint Range, California: Supplement 1 from "I. Geology of the Wildrose area, Panamint Range, California. II. Geochronologic studies in the Death Valley-Mojave Region, California" (Thesis)

The bedrock in the Wildrose area is predominantly a sequence of metamorphosed sedimentary and possible volcanic rocks that is more than 15,000 feet thick. All the metamorphic rocks are Precambrian in age on stratigraphic evidence. The rocks are divided into three age groups, early Precambrian, later Precambrian, and Precambrian (?), that are separated by unconformities. The early Precambrian Panamint metamorphic complex has been divided into two series that are separated by a profound unconformity. Small stocks and dikes of granitic rocks, which are presumably Cretaceous in age, intrude the metamorphic rocks. Tertiary sedimentary rocks and Quaternary alluvium are also present in the area. The structural features of the area are ascribed to four periods of deformation. The large folds in the early Precambrian rocks and associated minor folds were produced during the first two periods of deformation of early Precambrian age. Low angle faults are evidence of the third deformation which is considered to be Cretaceous in age. The fourth period of deformation produced high angle faults. Movement along the high angle faults began in late Tertiary time and has continued to the present. All the Precambrian rocks of the area have been affected by middle or lower middle grade metamorphism. Even though structural evidence suggests that metamorphism must have accompanied the earlier periods of deformation, the present mineral assemblages reflect the third period of deformation which, on the basis of mineral age measurements, was Cretaceous in age. Narrow contact metamorphic aureoles surround the larger masses of granite. Radioactive ages were measured in five areas in the Death Valley-Mojave Desert region. The rocks are Precambrian in age on stratigraphic evidence in three areas, the Wildrose area of the Panamint Range, the Mountain Pass district, and the Marble Mountains. The rocks in Joshua Tree National Monument and the Kilbeck Hills are presumably Precambrian, but no stratigraphic evidence of their age has been found. The geochronologic studies in the five areas indicate three distinct groups of K - Ar and Rb-Sr ages. Ages of approximately 1650 million years are obtained on metamorphic rocks and associated pegmatite s in the Mountain Pass district. Younger igneous rocks at Mountain Pass and in the Marble Mountains have age patterns that are interpreted to indicate intrusion in the 1350 to 1450 million year interval. Metamorphic rocks in the Wildrose area, Joshua Tree National Monument , and the Kilbeck Hills have ages in the 75 to 85 million year interval which are interpreted as the age of regional metamorphism related to the Cretaceous Nevadan orogeny. An age of 73 million years was obtained on a post-metamorphic granite

Hercynian granites and metamorphic rocks from the Mts. Papuk, Psunj, Krndija, and the Surroundi ng basement of the Pannonian Basin in Slavonija (Northern Croatia, Yugoslavia)

Hercynian crystalline complex of the Slavonian Mountains and surrounding basement of the Pannonian Basin comprises the following units: (1) anchimetamorphic and very low-grade metamorphic rocks with metabasic igneous rocks, (2)progressive metamorphic succession of greenschist and amphibolite facies, (3),migmatites, (4) S-type granitoids, and (5) I-type granitoids.In the paper is presented a petrological interpretation for each of the mentioned unit which is based on chemical composition of rock-forming minerals,petrographical and geochemical data including major and trace element contents,REE, and O and Sr isotopie composition.Numerous geochemical and petrochemical diagrams are presented for allthese rock groups as the basis for detailed genetic and geotectonic considerations

Distribution of Ordovician and Devonian metamorphism in mafic and pelitic schists from northern Vermont

^(40)Ar/^(39) Ar range from 471 to 439 my and confirm that Ordovician metamorphism is recorded from the Canadian border south to the Precambrian core of the Green Mountain Anticlinorium (GMA). Medium-high pressure (P) facies series metamorphism in the north and medium-P metamorphism to the south. Similar metamorphic ages and compatible estimates of T and P indicate mafic and pelitic rocks were metamorphosed together. Medium-P Devonian metamorphism has overprinted the Ordovician metamorphism in northern Vermont east and probably west of the GMA axis, resulting in conventional K/Ar, ^(40)Ar/^(39)Ar total fusion and plateau ages of 386 to 355 my on muscovite, biotite, and amphibole. --Modified journal abstract

Potassium-argon dating : principles, techniques, and applications to geochronology /

Bibliography: p. [227]-240